Sex-specific effects of psychoactive pollution on behavioural individuality and plasticity in fish

The global rise of pharmaceutical contaminants in the aquatic environment poses a serious threat to ecological and evolutionary processes. Studies have traditionally focused on the collateral (average) effects of psychoactive pollutants on ecologically-relevant behaviours of wildlife, often neglecting effects among and within individuals, and whether they differ between males and females. We tested whether psychoactive pollutants have sex-specific effects on behavioural individuality and plasticity in guppies (Poecilia reticulata), a freshwater species that inhabits contaminated waterways in the wild. Fish were exposed to fluoxetine (Prozac) for two years across multiple generations before their activity and stress-related behaviour were repeatedly assayed. Using a Bayesian statistical approach that partitions the effects among and within individuals, we found that males—but not females—in fluoxetine-exposed populations differed less from each other in their behaviour (lower behavioural individuality) than unexposed males. In sharp contrast, effects on behavioural plasticity were observed in females—but not in males—whereby exposure to even low levels of fluoxetine resulted in a substantial decrease (activity) and increase (freezing behaviour) in the behavioural plasticity of females. Our evidence reveals that psychoactive pollution has sex-specific effects on the individual behaviour of fish, suggesting that males and females might not be equally vulnerable to global pollutants.